1. Field of the Invention
The present invention relates to electronic imaging. More particularly, the present invention is related to an I-CIS (Industrial Camera Image Scanner) such as used for large flat panel inspection.
2. Related Background Art
A prior art camera image scanner configuration for industrial application is illustrated in FIG. A. Such industrial application includes, for example, the real-time inspection of large liquid crystal display (LCD) production panels, thin film solar panels and textile production webs. Here, an object surface located in an object plane is, while being illuminated by an Illumination Source, imaged by a charge coupled device (CCD) Image Sensor located at an “Imaging Distance” away from the object plane (along Z-direction). While not specifically illustrated here, to those skilled in the art a real inspection of the object surface can be accomplished by imaging the object surface on a scan-line by scan-line basis, with each scan line width labeled “Object Image Width” (X-direction), while providing a controlled relative motion (along Y-direction) between the object surface and the CCD Image Sensor. In an industrial application, the Object Image Width can be easily as large as 36″ to 72″. As the “Image sensor Width” of a single CCD Image Sensor is only in the range of 1″ to 2″ that is substantially smaller than the Object Image Width, an intervening focusing optical path with a Focusing Lens effecting a tiny magnification factor (1:72 to 1:18) is required between the object plane and the imaging surface of the CCD Image Sensor. Given the large Object Image Width and tiny magnification factor, the resulting Imaging Distance lies typically in the range of 10-30 cm.
FIG. B is a basic lens ray diagram for the focusing optical path of the prior art camera image scanner configuration of FIG. A. In addition to a Normal Imaging Light Ray along the Z-axis, a large number of Oblique Imaging Light Rays, each at an Oblique Angle θ from the Normal Imaging Light Ray, need to be focused between the CCD Imaging surface and the Object Plane as well. As the Oblique Angle θ becomes progressively larger toward the edge of the object plane, in the absence of any so-called f-θ compensation in the Focusing Lens design the Oblique Imaging Light Rays would become progressively out of focus as illustrated by the dashed arc tangential to the object plane. Given the imaging geometric parameters involved the Oblique Angle θ can become as large as 60 to 70 degrees where the degree of f-θ compensation can become unacceptable even with an expensive f-θ Focusing Lens. Additionally, it is known in the art that the imaging light intensity falls off toward the edge of the object plane following the cosine-law below:Intensity(θ)=I0×cos4(θ)Where I0 is the imaging light intensity at θ=0 degree. Thus, for example, at θ=60 degree Intensity (60 degree)=6.25%×I0. Such a loss of imaging light intensity near the edge of the object plane is most likely unacceptable in that its associated image signal level and signal-to-noise ratio (S/N) would be too low.
FIG. C illustrates another prior art wherein multiple line cameras (Camera-1, Camera-2, Camera-3, etc.) are juxtaposed with a camera pitch along the object image width for large flat panel inspection. Thus, for each camera, the magnification factor is proportionally increased while the Oblique Angle α, is proportionally reduced with the total number of cameras. With the reduction of Oblique Angle α, the problems of f-α compensation and image signal level fall-off at the edges are correspondingly reduced. However, accompanying the increasing number of cameras are disadvantages of bigger overall camera image scanner size, complication of required precision inter camera alignment for image stitching and inter camera imaging parallax error.
Accordingly, it is a primary object of the present invention to provide an Industrial Camera Image Scanner that is compact, having a short Imaging Distance and requiring only simple intervening focusing optical path and simple imaging signal processing.